Depends where the secondary head is.
Not many airfields, civil and military, have their own SSR. Bournemouth does, but it's in the minority. Many civil airports pipe in data from NATS SSR heads. Bristol, Filton, Cardiff? from Clee Hill in Shropshire, East Mids & Humberside from Claxby on the Lincolnshire wolds. Waddington's SSR is at Scampton, Cranwell & Coningsby at Cranwell. So, although you may be overhead the airfield, you may not be in the SSR overhead (which will be a blindspot).